The present invention relates, in general, to the field of integrated circuit (IC) devices having a need to conserve operating power. More particularly, the present invention relates to a short-circuit charge-sharing technique operative to conserve integrated circuit device operating power.
Power consumption is becoming one of the largest concerns for today's integrated circuit devices. Charge-sharing, or charge recycling, is a circuit design technique being explored in the industry to lower the power on many IC products. Conventional approaches to charge-sharing involve placing two circuit blocks in series with each other between power and ground. Each of the circuits then operates at approximately half of the total power supply level with the current consumed by one circuit being approximately the same as that consumed by the second. In operation, the current used by this first circuit is recycled and re-used by the second. An example of this technique is shown in FIG. 1 of Rajapandian et al., “High-Voltage Power Delivery Through Charge Recycling”, IEEE Journal of Solid-Sate Circuits, Vol. 41, No. 6, June 2006 at pg. 1401.
This conventional approach can be carried further to more than two circuits as is also shown in FIG. 2 of this same article wherein the various supply nodes are now labeled 3VDD, 2VDD and VDD as three similar circuits are placed in series. There are at least two limitations with this approach, one of which is that the two circuit blocks may not be balanced to where the current ITOP is not similar to IBOTTOM. This results in a drift of these internal power supply nodes and a shift in their levels depending on the amount of time each circuit is active. This can be overcome with a regulator and hold circuit however, efficiency of the charge-sharing operation quickly decreases with this current imbalance.
Another limitation of this technique exists when something other than an equal fraction of the supply voltage is desired to supply voltage for the circuit blocks. This can occur when the lower, or reference, voltage for one circuit block is not desired to become the supply voltage of the second circuit block.